This invention relates to high frequency, high power, semiconductive hybrid devices, or packages, wherein the undesired effects of particular components of common lead inductance are minimized, if not eliminated.
Typical examples of such prior art high frequency power transistor devices are shown in the U.S. Pat. Nos. 3,387,190 June 4, 1968, Winkler, 3,609,480, Sept. 28, 1971 Gerstner, 3,713,006 Jan. 23, 1973 Litty et al, 3,864,727 Feb. 4, 1975 Schoeberel, 3,996,603 Dec. 7, 1976 Smith and 4,042,952 Aug. 16, 1977 Kraybill.
In all of these devices the objectives tend to be the same which are those of eliminating, modifying or controlling in some way or other the common lead inductance of the transistor at the frequency desired and over a wide frequency band at appropriately high power levels. Constant and improved gain and improved input impedance are sought.
While the invention will be described in connection with bipolar transistor hybrid devices or packages, this is by way of example only, inasmuch as the invention may have application in appropriate instances to MosFets, or JFets or other semiconductive devices in similar configurations. When the expression transistor is utilized in this specification, it is intended to mean any of the foregoing stated devices.
Hybrid RF power, semiconductive devices, or packages, are well-known in the art. Typically such devices or packages include a transistor and an input capacitor mounted upon appropriately metallized surfaces of a beryllia substrate including a lead frame arrangement bonded to the metallized areas which includes input, output and ground portions or members. Appropriate wire bonds extend from the active portions of the transistor and capacitor to the various lead portions as is well understood. Such hybrid devices, or packages, may be characterized as having an input circuit and output circuit and a common circuit which includes common lead inductance.
The beryllia substrate is electrically insulating but thermally conducting and is usually mounted upon a relatively massive metallic heat sink. Appropriate ground connections may be made to the grounded heat sink. To complicate such structure further the input and output circuits usually comprise microstrip conductor means which include a metallic strip mounted on an insulating substrate whose impedances are matched to those of the input and output circuits of the transistor. In addition, the microstrip circuit devices may also be grounded to the metallic heat sink, for example, by wrap around metallizations.
All of these components must be considered to have their effect in the circuit in which the transistor is operating and as a practical matter reflect some part into the common lead inductance of the transistor circuit.
It is evident that the circuit approach is desirable to determine which component of the transistor, lead frame, metallizations, capacitor, substrate, heat sink and input and output microstrip conductors must be modified in order to achieve the optimum from a standpoint of minimizing the effects of the common lead inductance. The circuit approach to the problem is typified by the aforesaid U.S. Pat. Nos. to Litty et al 3,713,006 and Kraybill, 4,042,952. While in these examples of the prior art substantial progress has been achieved in minimizing the effects of the common leads inductance, all of the effects have not been eliminated particularly at the higher power levels and at the higher frequencies, for example, in the range of 400 mHz to one or more gHz.